1. Technical Field
The present invention relates to a light source device and a projector.
2. Related Art
A projector which includes a light source device, a light modulation device for forming image light corresponding to image information by modulating light emitted from the light source device, and a projection device for projecting the image light after expansion onto a projection surface such as a screen is known. The light source device of the projector contains a discharge-type arc tube such as an extra-high pressure mercury lamp in many cases. According to this type of arc tube, the temperature of the arc tube increases during light emission.
More specifically, the arc tube has a substantially spherical light emission portion into which a pair of electrodes and light emission substances such as mercury are sealed. During lighting of the arc tube thus constructed, the upper part of the light emission portion has the highest temperature, and the lower part of the light emission portion has the lowest temperature. When the high-temperature condition of the upper part of the light emission portion continues, the transparency of the arc tube easily decreases. Moreover, when the temperature difference between the upper part and the lower part increases, blackening easily occurs and often leads to deterioration of the arc tube.
For overcoming these problems, such a structure which directly supplies cooling air to the upper part of the light emission portion has been proposed (for example, see JP-A-2002-189247).
A lamp unit disclosed in JP-A-2002-189247 includes a discharge lamp containing a reflector and a power source bulb (arc tube), and a lamp holder to which the discharge lamp is attached. The lamp holder has a bottom support portion having an air inlet port, and an air direction changing plate is supported by the bottom support portion in such a condition as to be freely rotatable.
According to a projector disclosed in JP-A-2002-189247, the direction of cooling air is regulated by the air direction changing plate. The cooling air thus regulated is supplied via the air inlet port to a portion of the power source bulb above the bulb center as the portion where the temperature becomes high so as to cool the corresponding portion.
According to the projector shown in JP-A-2002-189247, cooling air can be supplied to the upper part of the light emission portion by rotation of the air direction changing plate either in a normal position where the projector is placed on an installation surface such as a desk, or in a suspended position where the projector is fixed to a ceiling or the like as the upside-down position of the normal position, for example.
According to the lamp unit disclosed in JP-A-2002-189247, however, cooling air is directly supplied to the high-temperature part close to the bulb center. In this case, the cooling efficiency lowers.
For promoting heat transmission at an improved heat transfer rate during cooling of the cooling target, there is a method which reduces the thickness of the temperature boundary layer of the cooling target to a thin film layer to promote heat transmission from the cooling target to cooling fluid, for example. According to this method, the flow speed of the cooling fluid is raised to a higher speed to lower the temperature of the cooling target based on the fact that the thickness of the temperature boundary layer is inversely proportional to the square root of the flow speed of the cooling fluid in the direction along the cooling target. For increasing the flow speed of the cooling fluid, the size of a fan supplying cooling air or the rotation speed of the fan needs to be increased when the cooling fluid is constituted by cooling air.
However, in case of the enlarged fan size, reduction of the size of the projector is difficult to be achieved. On the other hand, in case of the raised fan rotation speed, noise such as driving noise and wind noise produced by the fan increases. Accordingly, other structure which can improve the cooling efficiency for the arc tube has been demanded.